This invention relates to die apparatus of the so-called cross-head type wherein a layer of insulating material, or the like, is applied to a continuous filament such as an electrical wire, optical fiber, etc.
In typical cross-head dies a filamentary element is drawn axially through a die body as a coating material, such as molten plastic, is supplied to a cavity within the body through a radial opening therein. As the filament is drawn through a die orifice at the front of the body it is coated with the plastic, which dries to form a continuous insulating layer having a thickness dependent on the difference in diameters of the die orifice and the filament. Guide means within the die body provide axial alignment of the filament with the die orifice.
Applicant's U.S. Pat. No. 5,031,568 discloses cross-head die apparatus wherein internal elements are maintained in axially aligned relation by mating surfaces which are conically tapered about the central, longitudinal axis. Surfaces of an axial bore extending through the die body are tapered from a smaller diameter at their rearward ends. i.e., the end at which the filament enters, to a larger diameter at their front ends, i.e., in the direction of filament movement. This assembly of elements included a die member having an orifice at the forward end of the die body through which the coated filament exits the apparatus. When the elements are assembled, the exterior surface of the die member tapers from a smaller to a larger diameter from its front to its end, i.e., oppositely to the direction of taper of the internal bore of the body. The die member is positioned in a die holder having an internal surface of the same tapering configuration as the external surface of the die member, and an external surface tapering from larger to smaller diameters from front to rear, mating with the axial bore of the cross-head body. A threaded collar on the front of the body maintains the elements within the bore.
Other U.S. patents, such as U.S. Pat. No. 3,649,730 of Benteler et al, U.S. Pat. No. 3,947,173 of Dougherty, U.S. Pat. No. 4,165,957 of Kertacher and U.S. Pat. No. 5,108,683 of Anand, disclose cross-head extruding apparatus having elements with tapered external surfaces mating with tapered bores of other elements. A primary requirement of such apparatus is that the molten plastic be evenly distributed about the wire as it enters and passes through the die orifice. A number of arrangements, often requiring relatively complex and expensive elements and/or machining operations, have been proposed to achieve this requirement. It is also necessary to disassemble the components from time to time for purposes of cleaning, repair, etc. Since mating surfaces of the elements are often in tight engagement, with close tolerances, parts may tend to stick together and be difficult to disassemble.
It is a principal object of the invention to provide a tip holder element for use in a cross-head die to improve and promote uniformity of flow of a molten coating material about a filamentary member which is moved axially through the die.
Other objects will in part be obvious and will in part appear hereinafter.